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Conjuncevies vehicle transmission

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Unformatted text preview: Order: Carnivora Family: Viverridae –  one hypothesis of the source of SARS (Severe Acute Respiratory Syndrome) was from processing or consumpEon of civet meat –  another hypothesis: bats hOp://www.lexphoto.co.uk/ blogimages/civet%20that%20came %20to%20thecamp.jpg communicable diseases: STDs Sadava text p. 917: “About half of U.S. youth will contract an STD before the age of 25.” 1 0 37 >18 1 4 1 enrollment of this class: 367 #s in red, # of cases expected IN THIS CLASS •  Useful summary staFsFc similar to populaFon growth “R0” •  DefiniFon = the average number of secondary cases a typical infec6ous individual will cause in a completely suscep6ble popula6on •  Measure of the intrinsic potenFal for an infecFous agent to spread A measure of the potenEal for transmission The basic reproduc6ve number, R0, the mean number of individuals directly infected by an infec.ous case through the total infecEous period, when introduced to a suscepEble populaEon probability of transmission per contact R0 = p • c • d duraEon of infecEousness contacts per unit Eme InfecEon will ….. disappear, if R < 1 become endemic, if R = 1 become epidemic, if R > 1 •  If R0 < 1 then infecFon cannot invade a populaFon –  implicaFons: infecFon control mechanisms unnecessary (therefore not cost- effecFve) •  If R0 > 1 then (on average) the pathogen will invade that populaFon –  implicaFons: control measure necessary to prevent (delay) an epidemic p, transmission probability per exposure – depends on the infecEon   HIV, p(hand shake)=0, p(transfusion)=1, p(sex)=0.001   intervenEons o<en aim at reducing p   use gloves, screene blood, condoms c, number of contacts per Fme unit – relevant contact depends on infecEon   same room, within sneezing distance, skin contact,   intervenEons o<en aim at reducing c   IsolaEon, sexual absEnence d, duraFon of infecFous period   may be reduced by medical intervenEons (TB, but not salmonella) Endemic - Epidemic - Pandemic Cases R > 1 R = 1 Time R < 1   Endemic   Transmission occurs, but the number of cases remains constant   Epidemic   The number of cases increases   Pandemic   When epidemics occur at several continents – global epidemic Levels of Disease Occurrence Sporadic level: occasional cases occurring at irregular intervals Endemic level: persistent occurrence with a low to moderate level Hyperendemic level: persistently high level of occurrence Epidemic or outbreak: occurrence clearly in excess of the expected level for a given time period Pandemic: epidemic spread over several countries or continents, affecting a large number of people stay healthy out there!...
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